1. Field of the Invention
The present invention relates to a method for manufacturing a device and a lithographic apparatus.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
The known lithographic apparatus comprises a position measurement system for measuring the position of the substrate table in a certain number of degrees of freedom. Such position measurement system comprises a set of sensors, the number of sensors being at least equal to the number of degrees of freedom that is measured with the position measurement system. Typically the position of the substrate table is measured in six degrees of freedom (X,Y,Z, Rz, Ry, Rx). For instance, in the known lithographic apparatus an interferometer system with at least six sensors is used to measure the position of the substrate table. However, other configurations to measure the position of movable objects such as substrate tables and patterning device supports are known.
Since the requirements on product quality as well as resolution are continuously increasing, there is a demand for higher accuracy of the image projected on the substrate as well as reproducibility thereof (focus and overlay). In order to obtain such higher accuracy, it is desirable to measure the position of movable objects such as a patterning device support or a substrate table with high accuracy.